1. Field of the Invention
The present invention relates to motor drive control apparatuses. Particularly, the present invention relates to a motor drive control apparatus that is suitable for an input apparatus with a function of giving a force sense, which input apparatus couples a manual operation member to the axis of rotation of the motor to give the force sense to the operation member, and that is capable of suppressing the motor torque involved in an increase in current, flowing through the motor, based on the electromotive force of the motor when the operation member is manually operated to rotate the motor.
2. Description of the Related Art
Hitherto, motor drive control apparatuses that rotate direct current (DC) motors in both directions use motor drive circuits each having four switching elements connected to each other to form a bridge circuit. In the bridge circuit, a first switching element is connected in series to a third switching element between a power supply and a reference voltage point, a second switching element is connected in series to a fourth switching element between the power supply and the reference voltage point, and a DC motor is connected between the connection point between the first and third switching elements and the connection point between the second and fourth switching elements. The first and third switching elements are connected in parallel to the second and fourth switching elements. The first to fourth switching elements and the DC motor form an H-bridge circuit. In order to rotate the DC motor in a positive (one) direction, the first and fourth switching elements are turned on and the second and third switching elements are turned off. In contrast, in order to rotate the DC motor in a negative (the other) direction, the first and fourth switching elements are turned off and the second and third switching elements are turned on.
Various motor drive circuits using the H-bridge circuits are known. Examples of the motor drive circuits are disclosed in, for example, Japanese Unexamined Patent Application Publication No. 11-243696, Japanese Unexamined Patent Application Publication No. 11-215876, and Japanese Unexamined Patent Application Publication No. 06-237591. An input apparatus with a function of giving a force sense is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2003-22159 (corresponding to U.S. Pat. No. 6,854,352).
FIG. 4 is a circuit diagram showing the configuration of a motor drive circuit disclosed in Japanese Unexamined Patent Application Publication No. 11-243696.
In the motor drive circuit shown in FIG. 4, a first pair of switching elements 41 and 42 connected in series to a power supply 47, a second pair of switching elements 43 and 44 connected in series to the power supply 47, and a DC motor 45 and a current sensor 46 that are connected in series between the connection point between the switching elements 41 and 42 and the connection point between the switching elements 43 and 44 form an H-bridge circuit. The H-bridge circuit is provided with a driving unit including a controller 48 that outputs a driving signal, a pulse width modulation (PWM) signal, and a rotation direction signal, and a first AND gate 49, an inverter 50, a second AND gate 51, and a third AND gate 52 that electively supply the driving signal, the PWM signal, and the rotation direction signal to the first to fourth switching elements 41 to 44.
The motor drive circuit having the configuration in FIG. 4 operates in the following manner. In order to rotate the DC motor 45 in the positive direction, the controller 48 outputs a high-level rotation direction signal and a high-level driving signal. The switching elements 41 and 44 are tuned on and the switching elements 42 and 43 are tuned off to apply a current from the switching element 41 to the switching element 44 through the DC motor 45. This current serves as a current for rotating the DC motor 45 in the positive direction. In contrast, in order to rotate the DC motor 45 in the negative direction, the controller 48 outputs a low-level rotation direction signal and a high-level driving signal. The switching elements 41 and 44 are turned off and the switching elements 42 and 43 are turned on to apply a current from the switching element 43 to the switching element 42 through the DC motor 45. This current serves as a current for rotating the DC motor 45 in the negative direction. When the controller 48 outputs the PWM signal with the DC motor 45 rotating in the positive or negative direction, the average positive current for the DC motor 45, flowing through the switching element 42, is varied with the pulse duty indicating the on-off ratio of the PWM signal or the average negative current for the DC motor 45, flowing through the switching element 44, is varied with the pulse duty. The pulse duty of the PWM signal is controlled such that the average positive or negative current is equal to a target current.
FIG. 5 is a circuit diagram showing the configuration of a motor drive circuit disclosed in Japanese Unexamined Patent Application Publication No. 11-215876.
In the motor drive circuit shown in FIG. 5, a first pair of switching elements 61 and 62 connected in series between a power supply 66 and a ground point, diodes 61D and 62D connected in parallel to the switching elements 61 and 62, respectively, a second pair of switching elements 63 and 64 connected in series between the power supply 66 and the ground point, diodes 63D and 64D connected in parallel to the switching elements 63 and 64, respectively, and a DC motor 65 connected between the connection point between the switching elements 61 and 62 and the connection point between the switching elements 63 and 64 form an H-bridge circuit. The H-bridge circuit is provided with a driving unit including four switching-element drive circuits 67, 68, 69, and 70 and two OR circuits 71 and 72.
The motor drive circuit having the configuration in FIG. 5 operates in the following manner. In order to rotate the DC motor 45 rightward (in the positive direction), a control unit (not shown) outputs a right PWM instruction, stops the output of a left PWM instruction, and outputs a driving-direction switching signal. When the driving-direction switching signal is in a low level and the right PWM instruction is in a high level, the switching elements 61 and 64 are turned on and the switching elements 62 and 63 are turned off to apply a current IM to the DC motor 45 and to rotate the DC motor 45 rightward. When the right PWM instruction is in the low level, all the switching elements 61 to 64 are turned off to apply no current to the DC motor 45 and to stop the rotation of the DC motor 45. When the driving-direction switching signal is in the high level, the switching element 61 is turned on or off as the right PWM instruction is changed to the high level or low level, the switching element 64 is turned on regardless of the level of the right PWM instruction, and the remaining switching elements 62 and 63 are turned off. The current IM flows through the DC motor 45 to rotate the DC motor 45 rightward. When the right PWM instruction is in the low level, the free-wheeling diode 61D is turned on to apply the current MI through the DC motor 45 along a path indicated by a broken line and to rotate the DC motor 45 rightward. In contrast, when the control unit outputs the left PWM instruction and stops the output of the right PWM instruction, the current IM flows through the DC motor 45 in a manner substantially similar to the manner described above to rotate the DC motor 45 leftward.
FIG. 6 is a circuit diagram showing the configuration of a motor drive circuit disclosed in Japanese Unexamined Patent Application Publication No. 06-237591.
In the motor drive circuit shown in FIG. 6, a first pair of switching elements 81 and 82 and a current detection resistor 86 which are connected in series between a power supply 87 and a ground point, a second pair of switching elements 83 and 84 and the current detection resistor 86 which are connected in series between the power supply 87 and the ground point, and a DC motor 85 connected between the connection point between the switching elements 81 and 82 and the connection point between the switching elements 83 and 84 form an H-bridge circuit.
The motor drive circuit having the configuration in FIG. 6 operates in the following manner. In order to rotate the DC motor 85 in the positive direction, a control unit (not shown) supplies a high-level signal to the switching element 81, low-level signals to the switching elements 82 and 83, and a PWM signal to the switching element 84. When the PWM signal is in the high level, the switching elements 81 and 84 are turned on and a current is applied from the switching element 81 to the switching element 84 through the DC motor 85 to rotate the DC motor 85 in the positive direction. When the PWM signal is in the low level, no current is applied to the DC motor 85 to stop the rotation of the DC motor 85. In order to rotate the DC motor 85 in the negative direction, the control unit supplies the low-level signals to the switching elements 81 and 84, the high-level signal to the switching element 82, and the PWM signal to the switching element 83. When the PWM signal is in the high level, the switching elements 82 and 83 are turned on and a current is applied from the switching element 83 to the switching element 82 through the DC motor 85 to rotate the DC motor 85 in the negative direction. When the PWM signal is in the low level, no current is applied to the DC motor 85 to stop the rotation of the DC motor 85.
Each of the known motor drive circuits described above uses the PWM signal as a drive signal so as to drive the DC motor by using a constant current and attempts to cause the average driving current of the DC motor to be near to a target driving current by varying the pulse duty indicating the ratio of the high level of the PWM signal to the low level thereof. When the electromotive force of the DC motor is large, the current caused by the electromotive force is added to the average driving current, and the total current of the DC motor exceeds the control range of the pulse duty of the PWM signal, a driving current larger than the target driving current flows through the DC motor even when the ratio of the high level of the PWM signal to the low level thereof is set to 0%, or the PWM signal is always set to the low level, and, thus, the DC motor cannot be driven by using the constant current.
Particularly, when the DC motor is used for giving the force sense to an operation member, the above problem becomes noticeable. The force sense means the sense of force, such as a sense of click, which an operator receives via the operation member. The force sense is caused by, for example, a drag against the movement of the operation member at a predetermined position of the operation member, which drag is caused by controlling the DC motor coupled to the operation member. Since the operation member is moved simultaneously with the provision of the force sense when the operation member is manually operated, the DC motor is also driven to generate the electromotive force. When the electromotive force exceeds the target driving current, a current corresponding to the surplus electromotive force flows through the DC motor even with the pulse duty being set to 0% and, therefore, the torque corresponding to the flowing current is generated and the operator senses this torque. Since the electromotive force of the DC motor is varied with the operation speed by the operator and/or the characteristics of the DC motor, a constant force sense, for example, uniform motor torque, cannot be provided. As a result, the operator cannot obtain a superior operation sense.